(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Control of heavy infestations of purple scales on grapefruit trees"

LIBRARY 

STATE PLANT BOARD 

November 1953 E-870 



United States Department of Agriculture 

Agricultural Research Service 

Eureau of Entomology and Plant Quarantine 



CONTROL OF HEAVY INFESTATIONS 
OF PURPLE SCALES ON GRAPEFRUIT TREES 



By Herbert Spencer and Paul A. Norman 
Division of Fruit Insect Investigations 



In the Southeastern States heavy infestations of purple scales 
( Lepidosaphes beckii (Newm.)) develop on grapefruit trees and on 
some orange varieties, such as the Temple. This is particularly 
true in the coastal districts, where trees are usually sprayed once 
or twice each spring with copper fungicides and once with zinc and 
manganese compounds for minor element deficiencies. These com- 
pounds are added to regularly scheduled wettable-sulfur sprays, and 
the combination leaves heavy residues on the leaves and fruits. These 
residues favor increases of scale insects (Osburn and Spencer 1, 
Spencer 2), and the heavy infestations that develop are difficult and 
costly to control. 

For many years oil-emulsion sprays have been used for controlling 
these heavy infestations. They are effective when applied with thorough 
coverage before the infestation reaches damaging levels, but inasmuch 
as oil emulsion is incompatible with sulfur, it must be put on as an 
extra application, and this procedure increases costs. Also, when 
purple scale infestations develop in the fall and winter, oil sprays 
are objectionable because of harmful effects on fruit quality and color 
and the possibility of defoliation in cold or dry weather. Growers 
whose trees have heavy infestations in the fall often prefer to take 
the damage from the scales rather than to risk the damage from the 
oil spray and increase costs by using it. 

Preliminary experiments conducted during 1949 and 1950 (Spencer 
_et aL 3) indicated that parathion had great promise. Two sprayings 
with 1 pound of 15-percent wettable parathion per 100 gallons of water, 
in March and July, allowed only a slight increase in infestation through 
the year. It was evident, though, that further work was needed to 
determine the number of sprayings necessary each year, and the con- 
centrations, to reduce the infestations to satisfactory levels and to hold 
them there. For this work a, grove of Ruby grapefruit trees near Fort 
Pierce, Fla., was selected.-^ 



\j Norman G. Platts was the grower cooperator. 






on Ji 
as 1-1 



th one or 

~>0 



gallons 
in spray on- - 


nbers of living purple scales 
per leaf on- - 


M J 8 


July 10 


Ju. 


N 



1 



1 





1 
1 


2 





d for signif: 
1 

• l % Level 



. r >7 


.81 


1. 


13. 


3.98 


9.33 




. 




.65 


15/ 




3.84 




5.13 





1/ Bel 



■ 

■ 
■ 



3 - 



Experiments in 1951 

In 1951 the same trees were used, and the six programs were 
1-2-0, 2-0-0, 1-1-0, 1-0-2, 0-2-0, and 1-1-1. The postbloom spray 
was applied on April 2, the summer spray on June 1, and the fall spray 
on November 7. 

As shown in table 2, single applications of sprays containing 2 pounds 
of 15-percent wettable parathion per 100 gallons, whether made in 
April or in June, permitted increases in infestation. The 1-2-0 pro- 
gram gave good early and midseason control, but allowed some fall 
buildup. The same was true of the 1-1-0 program, except that the 
buildup was greater in the fall. The 1-0-2 program gave good fall 
cleanup, but allowed too much buildup in the summer. The best pro- 
gram in 1951 was three applications of the 1 -pound dosage, which 
reduced an infestation of 25 scales per leaf to around 4, and held it 
there throughout the year. However, 4 scales per leaf is too high. 



Table 2. --Control of purple scales on grapefruit trees with one, two, 
or three sprays of parathion applied in 1951 



Pounds of 15-percent wettable 

parathion per 100 gallons 

in spray on-- 


Numbers of living purple scales per leaf on-- 


April 2 


June 1 


Nov. 7 


Nov. 20, 
1950 


June 1, 
19511/ 


Oct. 17, 
1951 


Jan. 5, 
1952 



1 


2 





20.81 


2.29 


1.34 


6.07 


2 








13.91 


.50 


8.22 


14.53 


1 


1 





9.33 


1.47 


2.67 


9.10 


1 





2 


22.42 


3.43 


14.89 


.52 





2 





10.65 


8.14 


3.15 


11.16 


1 


1 


1 


25.22 


3.27 


4.35 


3.95 



Difference required for 
significance: 

At 5% level 

At 1% level 



7.31 

9.77 



1.52 
2.03 



3.00 
3.99 



4.02 
5.36 



\j Before spraying. 









: ■ 
, 1-1-2, 1-2 

8, 

em 

mounts ( 



hree 



ns 

Digitized by 









! 



■ 

-- 

- - 



he Internet Archive 



n20 






3 



1 




1 


. 


. 




1 










1 




. 




1 
















1 1. 




1 


1 




































. 






1 1 



I 

1 









http://archive.org/details/heavyinOOunit 



- 5 - 



Discussion 

All the parathion spray programs described above were safe for 
trees and fruit, and the best of the programs prevented damage from 
purple scales. 

These experiments suggest that, on grapefruit and orange trees 
sprayed with copper and nutritional materials, 2 pounds of 15-percent 
wettable parathion be added to the postbloom combination spray and 
1 pound each to the summer and fall wettable-sulfur sprays. After 
the first year 1 pound in each of the postbloom, summer, and fall 
sprays will probably be sufficient for year-round control of these 
heavy infestations. 

Literature Cited 

(1) Osburn, Max R., and Spencer, Herbert 

1939. Effect of spray residues on scale-insect populations. 
Jour. EcoruEnt. 31: 731-732. 

(2) Spencer, Herbert 

1939. Increases in citrus scale-insect infestations from heavy- 
residue and from copper spray mixtures. Jour. Econ. 
Ent. 32: 686-688. 

(3) Osburn, Max R., and Norman, Paul A. 

1952. Control of purple scale on citrus with parathion. U. S. 
Dept. Agr. Cir. 896, 10 pp. 






: -2 62